Network Attached Storage Round-Up (Part 2) - Limitations Of NAS, NAS Noise And Power

5/25/2012 5:47:26 PM

Limitations Of NAS

Although extremely useful devices, there are some limitations to NAS drives. In larger networks with a high volume of simultaneous I/O requests, a typical affordable NAS box is not going to be able to provide adequate performance. Their built-in CPUs will be too limited in performance and if over stretched will slow to a crawl. The CPU and network hardware in a NAS is also rarely upgradable, because its single-purpose CPU is hard-wired into the unit and the software stored on a firmware ROM chip. While it's possible to spend a lot of money on more powerful NAS boxes with the capacity to handle huge quantities of traffic, the lines between server and NAS begin to blur considerably, especially in terms of cost.

Description: Caringo Smashes Limitations of Block-Based NAS

Caringo Smashes Limitations of Block-Based NAS

In a home environment, these limitations are unlikely to be important, since high-volume simultaneous I/O traffic will be rare. A limitation that will be more important is one of actual transfer rate, as it's easy to fall into the trap of assuming a NAS box will be as fast as an internal hard drive. Although some NAS boxes offer great performance, some will only transfer data at 5-IOMB/s or, in the case of some manufacturers' offerings, even less than this. While this kind of transfer rate will not be a problem for streaming SD video to a single system, it won't have the bandwidth available to serve two streams simultaneously. Even for the best NAS boxes, you will need to invest in your home network infrastructure to ensure that the transfer rate is not limited by the 100Mbps networks most of us use at home. This situation only becomes slower if you are limited to wireless.

These limitations in speed are not caused by the hard drive technology within, because even a modest 7200rpm hard drive can sustain transfer rates of well over 100MB/s. Many NAS drives boast of a 'fast SATA interface' or 'gigabit connection', and yet still fall well short of even 100Mbps network performance. This limitation is caused by a bottleneck at the NAS drive's CPU, which can only process data requests so fast. Seeing as these are a tiny fraction as powerful as the CPU at the heart of your home PC, it's not entirely surprising you don't get the same level of performance. In this day and age of ultra- fast computers, it's easy to forget just how much overhead is required for good performance over a proper network!

Making Use Of Old Drives

Description: Synology

Many enthusiast users have more than one spare hard drive knocking around, in which case these can be recalled to service as a NAS solution. Almost all NAS manufacturers offer drive-free caddies that will allow you to plug in an existing SATA drive and convert it to NAS duties. Some of these are extremely affordable, costing less than $80. You invariably get what you pay for, however, so be sure to read some reviews before parting with your cash. We've tested some cheap NAS enclosures before that feature shockingly slow firmware, appalling transfer rates and unreliable software. One of our favourite enclosures is the Synology DS110J, a single bay drive-less enclosure with outstanding software and performance. These enclosures can achieve over 60MB/s in read and around 40MB/s in write when connected to a suitable gigabit network - impressive for such a modest asking price. They have been replaced in Synology's line-up with the newer DS112J, meaning they can be snapped up for a bargain price of less than $128 if you shop around!

If you do need new drives to go with your NAS, however, don't automatically assume you'll always get a better deal by sourcing the enclosure and the drives separately. Since the hard drive crisis hit, we've seen several cases where it's actually cheaper to buy a NAS with the drives you need rather than source the constituent components separately.

As most NAS drives are bottlenecked by the speed of your network or by the performance of their own internal processing and memory constraints, you don't need to invest in extremely fast hard disk drives to maximise their performance. It's much better to invest in drives that prioritise quietness, reliability and power efficiency like the Western Digital Caviar Green or Samsung 5900rpm Ecogreen products. These drives still provide 100MB/S+ performance when reading or writing, which is more than enough for a NAS application. They're also significantly quieter than 7200rpm models and will save power as well. Most of us leave NAS boxes permanently turned on, so although a 3-4W saving in power isn't that relevant in the scope of running a desktop PC, it's valuable for a NAS, which is designed to be left on 24/seven. All too often we see even professional reviewers recommending faster hard drives for improved NAS performance when in actual fact this will almost never make any difference to the performance of your device.

NAS Noise And Power

The low noise level and power consumption of NAS drives is a major attraction compared to a server, but that doesn't necessarily make them silent.

Most multi-drive NAS boxes have at least one cooling fan to keep the drives happy, with larger units usually incorporating several. Conversely, most single-drive NAS units do not require fans, because the thermal dissipation of just a single disk can be capably handled passively.

If you're concerned with your green credentials, try to choose a NAS that has built-in power saving. This will allow it to power down the drive(s) when the unit isn't being accessed, reducing consumption by however much power is being consumed to keep the drive motors running (typically 8-12W per drive depending on the model being installed).

Description: NAS Noise And Power

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